1. Field of the Invention.
This invention relates generally to apparatus for drilling a well or bore hole in the earth using a plurality of drill pipe sections joined in end-to-end relationship with a cutter head or drill on the lowermost end and relates particularly to apparatus for selectively supporting or holding the drill string and assisting in "breaking" the connection between pipe sections when the string is being disassembled.
2. Description of the Prior Art.
In the past, most vertically disposed drill rigs have included a drill table located close to the earth and having an opening through which the drill string extended. These prior art structures usually have included a clamp mechanism located adjacent to the drill table and such clamp mechanism was arranged so that a pair of jaws could be actuated to clampingly engage a pair of opposed flattened portions adjacent to the upper end of each drill pipe section. These clamping mechanisms were satisfactory for holding the drill string; however, it was usually necessary to provide a separate break wrench to start separation of the upper drill pipe section from the remainder of the string during disassembly. The break wrench has been necessary since each drill pipe section usually has a reduced threaded stud which engages a threaded opening in the end of the next adjacent pipe section. During the drilling operation, the drill string is rotated in a direction to tighten the cooperating screw threads. The break wrench ordinarily is sufficient to start separation of the drill pipe sections but when such wrench fails to break the threaded connection, substantial manual labor has been required with the assistance of chains or large stillson type wrenches to break the threads.
Some efforts have been made to improve the conventional clamping mechanisms by providing selectively operable holding wrenches to hold the drill string against rotation while the threaded connection has been broken either by the power plant mounted on the drill rig or by a break wrench. Some examples of the prior art are disclosed in the U.S. Pat. Nos. to Alexander 3,239,016; Back 3,708,024; Coyne 3,771,389; and Dyer Re. 28,351.